heya,
i aquired a vintage heathkit amp that has been upgraded and recapped by a forum member less than a week ago.
there seem to be a few issues with it though.. one of which is that there is sometimes a low pitched vibrating sound coming from the chassis or tubes themselves.. kind of sounds like dry ice on a spoon if you have reference to that.
i was told the amp had a hot plating issue at one time but it was supposedly resolved. could this be that issue reappearing?
i'm also getting occasional popping through the speakers.. sometimes left channel, sometimes right and sometimes both.
it has blown a fuse also.. the power fuse from the back. i was told to switch to a 2 amp slow blow and it probably wont happen again.. to be on the safe side i replaced with a quick blow like it came with and its been okay so far. (1 day)
i thought the problems may be heat related but i've taken extensive measures to make sure the amp gets plenty of air now and it is running cool but problems persist.
otherwise the amp plays very nicely. i am getting some sweet mid-highs, although the low end is a but lacking but i hear this is somewhat common with tubes.
do these symptoms sound familiar to a certain problem tubes or tube amps run into? do they sound like minor issues you guys would just live with or do you think they should definatly get looked after before something worse crops up.
i aquired a vintage heathkit amp that has been upgraded and recapped by a forum member less than a week ago.
there seem to be a few issues with it though.. one of which is that there is sometimes a low pitched vibrating sound coming from the chassis or tubes themselves.. kind of sounds like dry ice on a spoon if you have reference to that.
i was told the amp had a hot plating issue at one time but it was supposedly resolved. could this be that issue reappearing?
i'm also getting occasional popping through the speakers.. sometimes left channel, sometimes right and sometimes both.
it has blown a fuse also.. the power fuse from the back. i was told to switch to a 2 amp slow blow and it probably wont happen again.. to be on the safe side i replaced with a quick blow like it came with and its been okay so far. (1 day)
i thought the problems may be heat related but i've taken extensive measures to make sure the amp gets plenty of air now and it is running cool but problems persist.
otherwise the amp plays very nicely. i am getting some sweet mid-highs, although the low end is a but lacking but i hear this is somewhat common with tubes.
do these symptoms sound familiar to a certain problem tubes or tube amps run into? do they sound like minor issues you guys would just live with or do you think they should definatly get looked after before something worse crops up.
Due to the age of the amplifier, I would be very suspicious of every electrolytic capacitor in the unit. For reliability reasons, I would replace those as a preventive maintenance measure.
As for the "hot-plating" issue and limited bandwidth, it sounds like signal path coupling caps. Probably the ones following the phase inverter. They sometimes short and pull plate current through grid of the power tube(s). The power tube plates will glow because they are not biased.
These are speculative ideas since I am not intimately farmiliar with the unit and, do not have a schematic to look at.
Regards,
Al
As for the "hot-plating" issue and limited bandwidth, it sounds like signal path coupling caps. Probably the ones following the phase inverter. They sometimes short and pull plate current through grid of the power tube(s). The power tube plates will glow because they are not biased.
These are speculative ideas since I am not intimately farmiliar with the unit and, do not have a schematic to look at.
Regards,
Al
Like the previous posters said, maybe you have two unrelated problems. I've found that intermittent popping can be bad contacts on the tube bases. Can be solved, as said, by tightening tube pins, replacing sockets or just going over all the pins again with a soldering iron - sometimes the solder cracks and you get an intermittent that you can't see with the naked eye. I guess hot plating - term I've never heard of before - means the plates of the output tubes once got hot, probably through a capacitor or resistor being out of spec or non-functional, so that's another problem.
Sputtering?
Many things could cause these symptoms. From your description it sounds like an intermittent connection as others have posted, either and/or bad sockets, bad/cold soldier joints, failing coupling/PS smoothing/bypass caps, bad tubes etc. Given the age of this dear to our hearts but old Heathkit; it may need a good overhaul! Especially replacing the PS caps and coupling caps, inspecting every soldier joint, checking for loose tube socket pins (not making good contact with the tube pins), off value resistors, those old carbon composition resistors are notorious for drifting off value with age and heat.
Yes and no.
Hot plating...? is an over current condition i.e. under biased, too much current passing through the tube and exceeding the plate dissipation rating (watts). Now when in that condition you may hear a sputtering sound. Vibrating as you have described it; could it possibly be 'motorboating'...?, which is a very low frequency oscillation around 1Hz to 2 or 3Hz caused usually by a bad or failing power supply (PS) capacitor. A bad layout or circuit design can cause this but it's probably not applicable in your case unless someone before you has modified the amplifier circuitry.
As for 'popping' the fuse, this is indicative of excessive current being drawn. If you have a schematic or if not the model number; I may have the schematic as I have schematics for quite a few Heathkit amplifiers on my computer. Then we could possibly help you better. Also what and where any modifications/upgrades were done by the "other"
forum member would be of great help! 
No! "We" would not live with this, no way!
Some of us would end up in the hospital from beating ourselves up trying to figure out what's wrong or go crazy trying to live with it! 
We would not consider these to be minor issues and if the output tube plates are glowing orange and popping fuses this would be a serious condition! And please don't be tempted to use higher rated fuses or bypassing them!
From your post you have not been tempted to do so, very good!So if you can come up with a schematic or model number that would be great! Hope I've helped you some way!
Cheers
Wayne
i dont think the tube plates themselves glow too much.. just the filiments of the tubes i guess so that sounds right.. the left channels 7199 tube filiments do seem to glow a bit dimmer than the rest though..
they are rogers, philco, rca, ge, sylvania and the it looks like no name "Japan" 6BQ5's brands.. all mixed together but the voltages or tube properties have been matched from what i have been told.
the tubes that are supposed to compliment this amp are 7199, EL84/6BQ6 and a GZ34/5AR4 but the ladder was replaced with something less powerful from what i understand due to avaliability issues.
the vibration i mentioned does not only occour when i turn the amp on and off.. it usually happens for 5 or 10 mins at a time, stops and starts again at some arbitrary moment.
the pop/crackle in the speakers occours wether the tubes are vibrating or not.. seems like at least once every 3-4 mins there is some kind of noise transmitted.
i've tried surge protected outlets as well as directly to the wall with no difference.
i think i'll take it back to the forum member and see if he cant figure it out.. hopefully it is just a minor tube or connection issue.
they are rogers, philco, rca, ge, sylvania and the it looks like no name "Japan" 6BQ5's brands.. all mixed together but the voltages or tube properties have been matched from what i have been told.
the tubes that are supposed to compliment this amp are 7199, EL84/6BQ6 and a GZ34/5AR4 but the ladder was replaced with something less powerful from what i understand due to avaliability issues.
the vibration i mentioned does not only occour when i turn the amp on and off.. it usually happens for 5 or 10 mins at a time, stops and starts again at some arbitrary moment.
the pop/crackle in the speakers occours wether the tubes are vibrating or not.. seems like at least once every 3-4 mins there is some kind of noise transmitted.
i've tried surge protected outlets as well as directly to the wall with no difference.
i think i'll take it back to the forum member and see if he cant figure it out.. hopefully it is just a minor tube or connection issue.
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